A plate cylinder and a blanket cylinder are adjusted in phase relationship thereof by the adjustment of the circumferential register. This adjustment thus effects a relative movement between the printing plate of the plate cylinder and the sheet in or opposite to the sheet travel direction.
Costly differential transmissions or gear units, such as planetary gear units or axially displaceable gearwheels with helical gearing, have become known heretofore for this purpose, in order to enable adjustment while the machine is running, yet only within a relatively small range.
In the case of smaller machines, gear drives with at least two intermediate gearwheels are known, above all, the two gearwheels being displaceable together with their bearings, thereby permitting a circumferential-register adjustment to be made. In constructions of this kind, the bearings of the intermediate gearwheels are correspondingly unstable. It is also possible for a circumferential-register setting to be made by adjusting the front lays, if the run or travel of the paper enables this. The most cost-effective and conventional adjustment device employs gearwheels rotatable in phase relationship thereof with respect to the cylinder, which must be released for the adjustment and locked again after the adjustment. Such devices for circumferential-register adjustment are able to operate only when the machine is stopped. Readjustments thus require adequately frequent stopping and restarting of the machine which demands a relatively large expenditure of time, and occasions much waste formation.
The foregoing details regarding the prior art correspond to the practical construction of conventional or marketable machines.
A construction which is especially problematic is that of a circumferential-register adjustment device in printing units for the printing of an additional color, so-called satellite printing units, which are removably or swivellably fastened to the frame of a sheet-fed rotary printing press and are brought into an operating position only when required. In satellite printing units, the components for circumferential-register adjustment contribute significantly to the undesired increase in the weight of such a printing unit and, in so doing, also raise its level of instability.